About 6 months ago I had a root canal and crown put on. About a week ago that tooth started getting sore. What is the problem?

Your best to go visit the Dentist to ensure that you don't have an infection under the crown. They should be more then happy to treat you as a follow up from the treatment.

Hi, smalltown,
I agree with your other answer of see your Dentist; it could be infection.
I had many root canals over the past years, with some crowns, bridge work, etc, and guess I was just plain lucky... no pain afterwards.
The only time I had a problem was when some decay eventually got under the crown, at the base of the remaining parts of the tooth.
It doesn't seem likely, though, to be decay.
Best of luck.

This answer assumes that your root canal was properly done.

All dental prosthetic must be checked for sharp edges which might prove irritating to soft tissue. This checking is initially done at the dental laboratory where the prosthetic is made. However, sometimes technicians will forget to check for these edges or a very small one, which your gum might notice but they don't, is impinging on the gumline. One thing to remember about a root canaled tooth, however, is that the nerve is no longer there. So the pain felt has to be coming from the surrounding tissue whether it be soft of bone which makes the whole area seem sore. As the other posters said, the best is to ask your dentist. He can will determine what tissues are involved and whether the cause is infection, sharp edges, or perhaps simply a bad crown fit.

BTW

Some time ago, I had what I was told was a tumor or abscess next to my upper first bicuspid. The dentists assumed this since they had not ordered a biopsy. After they ruined the tooth with hasty, careless, and unnecessary treatment which made crowning impossible, they told me that now I needed to have it pulled. The doctor doing the pulling, an oral surgeon, decided to do a biopsy. When he did, it turned out that all I had was an irritated salivary gland. So if your problem turns out to be a growth, don't accept tongue-in-cheek explanations which are really mere opinions or educated guesswork. Respectfully request a biopsy.

Thanks for your replys. I did go to a root canal specialist, and he told me that the infection was from a leakage of the material they put into the root. He gave me a low success rate for a re drill because it seems the tooth originally had a crack in it. Debating now to have it pulled or try the reem out procedure.

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My recently crowned back molar gave me pain for a week recently,though it had been on for a month with no trouble,what gives?